Due date guide
Understanding your estimated due date
Your estimated due date (EDD) is the single most-asked-about number in early pregnancy. It anchors your prenatal schedule, your scans, and the countdown to meeting your baby – but it is an estimate, not a deadline.
Naegele's rule
The standard formula takes the first day of your last menstrual period, adds one year, subtracts three months, and adds seven days – which works out to roughly 280 days. It assumes a regular 28-day cycle with ovulation on day 14.
Why cycle length matters
If your cycles run longer or shorter than 28 days, you ovulate earlier or later – which shifts your due date. This calculator adjusts for your average cycle length so the estimate fits your body rather than a textbook average.
Conception and IVF dating
If you know your conception or ovulation date, counting 266 days forward gives a tighter estimate. For IVF pregnancies the date is even more precise: the transfer day and the embryo's age (3-day or 5-day) pinpoint conception almost exactly.
Why your due date can change
Early in pregnancy your provider may revise the date after a dating ultrasound. Between 8 and 13 weeks, measuring the baby's crown-rump length predicts gestational age within a few days – more reliably than LMP for many people, especially with irregular cycles. If the ultrasound and your LMP disagree significantly, the scan usually wins.
Full term is a window, not a day
A pregnancy is considered full term from 39 weeks. Babies arriving from 37 to 42 weeks are all within the normal range, so treat your due date as the centre of a window rather than a fixed appointment. Use it to plan, pack, and prepare – then stay flexible.